Field of the Invention
The present invention relates to a printed wiring board on which a semiconductor device is mounted, a semiconductor device mounted on a printed wiring board, and a printed circuit board including a printed wiring board and a semiconductor device.
Description of the Related Art
In recent years, multi-functionalization of electronic apparatuses has been accelerated. Accordingly, in a semiconductor device mounted on a printed wiring board within the electronic apparatus, input terminals or output terminals (input/output terminals) that input or output signals have a tendency of increasing in number to realize various functions. Moreover, as performance of the electronic apparatus has been improved, a bandwidth for signal transmission of an electric signal has been increased in the semiconductor device mounted on the printed wiring board within the electronic apparatus. In order to increase the bandwidth for signal transmission, a method of providing a plurality of signal lines is used, which tends to increase the number of the input/output terminals of the semiconductor device. A means for securing the required number of the terminals for the semiconductor device includes a method of increasing an area of a wiring substrate of the semiconductor device, and a method of increasing the number of terminals per unit area by reducing intervals between the terminals.
However, as the area of the wiring substrate of the semiconductor device is expanded, a cost or a size of an apparatus on which the semiconductor device (printed circuit board) is mounted becomes larger. In addition, too short intervals between the terminals have a risk of lowering mounting reliability of the semiconductor device.
In Japanese Patent Application Laid-Open No. 6-069371, as a method for increasing the number of the terminals per unit area in the wiring substrate of the semiconductor device while securing intervals between the terminals in the semiconductor device, a method of arranging adjacent terminals so as to form an equilateral triangle has been proposed.
However, Japanese Patent Application Laid-Open No. 6-069371 describes the terminals to be arranged in an equilateral triangle, but does not describe how the terminals arrayed in an equilateral triangle are arranged relative to one of four sides of the wiring substrate having a substantially quadrangular shape in the semiconductor device.
In a typical semiconductor device, the terminals being adjacent to each other are arranged so as to form a square, and a terminal group including the plurality of terminals is arranged so as to fill a rectangular region so that intervals between the terminals are secured. In this case, one of four sides of the rectangular region and one side of the square of the terminal array are arranged so as to be parallel to each other. Accordingly, also in the semiconductor device described in Japanese Patent Application Laid-Open No. 6-069371, it can be considered that one side of the rectangular region in which the terminal group is arranged and one side of the equilateral triangle of the terminal array are arranged so as to be parallel to each other.
With such terminal array, in the printed wiring board, a difference in wiring density is generated between leading wires led out from one side of a rectangular region surrounding a land group to which the terminal group of the semiconductor device is coupled, and leading wires led out from an adjacent side. Leading directions in which the leading wires are led out are thus restricted, lowering the degree of freedom in design. Therefore, there has been a need to reduce a difference in the number of leading wires caused between the leading directions in the printed wiring board.
In addition, in the printed wiring board, the aforementioned land group array is capable of increasing the number of lands constituting the land group, but is not capable of sufficiently increasing the total number of the leading wires led outside from the rectangular region surrounding the land group.
An object of the present invention is to provide a printed wiring board, a semiconductor device, and a printed circuit board configured to maintain a terminal density per unit area and reduce a difference in the number of leading wires caused between the leading directions in the printed wiring board so that the degree of freedom in design is improved and the total number of leading wires is increased.